STUDY OF SEED-BORNE FUNGAL PATHOGENS OF KATARIBHOG RICE AND COMPARISON OF FIELD INTENSITY WITH LABORATORY COUNTS

Abstract

Eight landraces of fine aromatic Kataribhog rice were grown to investigate the prevalence of seed-borne fungal pathogens Pyricularia grisea, Bipolaria oryzea, Alternaria padwickii and Curvularia spp. during 2010 and 2011. The landraces viz. Philippine katari, Radhunipagal, Bolder, Zota katari, Tajmohal, Zira, Behulabasor and Badhua were used in this investigation. Disease severities in field level were recorded on leaf blast, neck blast, node blast, brown spot and spotted grains at different growth stages of rice viz. 80 days after transplanting for leaf diseases and 30 days after heading for neck blast, node blast and grain spot. The disease severity of leaf blast, neck blast and node blast were found significantly different among the landraces during 2010 and 2011. The blast incidence of mother crops during 2010 ranged from 19.22 to 26.30% in leaf, 23.27 to 64.89% in neck and 15.19 to 25.45% in node. In the subsequent crops of 2011, the disease severity of blast ranged from 19.21 to 34.60% in leaf, 21.54 to 60.48% in neck and 15.98 to 31.77% in node. The yield losses due to neck blast were noticed 13.26 to 36.99% and 12.28% to 34.48% during 2010 and 2011, respectively. The highest yield loss was recorded 36.99% in Zira katari in 2010 and the lowest 12.28% in Philippine katari in 2011. The growth of Pyricularia grisea was absent in the blotter test but the seeds were found to be presence of conidia ranged from 6.38 to 10.77 per 50 seeds in the washing test. Regarding brown spot severity in the field level ranged from 26.60 to 46.76% in 2010 and 28.28 to 48.45% in 2011. The prevalence of Bipolaris oryzae infected seeds ranged from 8.64 to 18.37% by blotter test. The results obtained in the comparison of the field intensity and seed infection by blotter method reflect correlation, furthermore, special interest also show the presence of conidia of Bipolaris oryzae in the washing test. Practically all the seed samples recorded higher number of conidia ranged 69.77 to 107.23 per 50 seeds. The growth of Alternaria padwickii and Curvularia spp. were also absent in the blotter test but the seeds were found to be presence of conidia ranged from 3.36 to 7.52 and 8.62 to 16.55, respectively per 50 seeds in the washing test. The severities of grain spot at maturing stage of Kataribhog rice were ranged from 19.88 to 64.94% in 2010 and 23.83 to 70.82% in 2011. Two sets of study were conducted concurrently on the physical quality of seed and seedling status. In one, seeds were first categorized into healthy seeds, discolored seeds, spotted seeds and unfilled grains for dry inspection. The apparently healthy seeds were found 2.50 to 70.25 % and unfilled seeds 3.50 to 13.25%. The results obtained on discolored and spotted seeds were in the following three categories; I: < 20% severity found 0.00 to 8.25% discolored seeds and 2.25 to 45.50 % spotted seeds; II: 20 to < 50% severities found 0.75 to 10.75% discolored seeds and 2.20 to 27.25 % spotted seeds; III: > 50% severities found 1.25 to 7.5% discolored seeds and 1.50% to 18.25 % spotted seeds. In the second set, seeds of the samples were sown directly in the soil, hundred seeds per tray. The germination ranged 87.00 to 93.00%, abnormal seedlings 18.00 to 48.00%, infected seedlings 16.00 to 38.00% and dead seeds 7.00 to 13.00%. The yield of per unit area ranged from 143.5 to 315.60 g/m” and per hector 2.01 to 3.28 t/ha during 2010 where the yield per unit area 133.50 to 302.30 g/m? and yield per hector 1.81 to 3.21 t/ha during 2011. The average percent yield gap among the landraces was 77.34%. Finally, the yield gap value indicated that there was much risk of severities of the fungal diseases for all landraces of Kataribhog rice.